Stress Relaxation in Bolted Flange Joints — PatSnap Eureka
Stress Relaxation in Bolted Flange Joints at Elevated Temperature
A time-dependent failure mode driven by creep in bolts, gaskets, and flange bodies causes progressive loss of clamping force and ultimately leakage. This report synthesises patent and literature evidence from 1957 to 2025 to characterise causes, mechanisms, and engineering countermeasures.
Four Interacting Phenomena Drive Clamping Force Loss
Bolted flange joints under elevated temperature are subject to a combination of thermally driven degradation mechanisms that reduce the initial assembly preload over time. The retrieved dataset consistently treats the flange-bolt-gasket assembly as a coupled mechanical system requiring deformation compatibility analysis to predict joint behaviour over long service periods.
Differential thermal expansion between bolts, flanges, and gaskets is the first driver: components made from materials with different coefficients of thermal expansion (CTE) expand at different rates when heated, altering the clamping force balance established during cold assembly. A 2021 steam generator study demonstrated that at elevated temperature, bolts expand more than flanges, reducing gasket contact stress and risking leakage.
Creep of bolts, gaskets, and flange body causes each component to deform slowly and permanently under sustained stress, redistributing and ultimately reducing the load on the gasket contact interface. Gasket creep displacement is modelled as a logarithmic function of time; bolt creep is proportional to bolt effective length and creep rate; flange creep is computed via deflection angle integration. Research published by ASME and documented in the 2023 Hefei General Machinery Research Institute patent confirms that no single component alone determines stress relaxation — deformation compatibility of all three simultaneously governs gasket residual stress evolution.
Stress relaxation of the gasket — particularly for viscoelastic types such as spiral wound, flexible graphite, and elastomeric — involves time-dependent reduction in contact stress even under fixed strain conditions. The 2025 East China University of Science and Technology patent notes that high temperature accelerates gasket creep-relaxation and aging, reducing elasticity and sealing capacity. Gasket characterisation is identified as a bottleneck: creep-relaxation parameters are poorly characterised, especially for metallic and composite gaskets at temperatures above creep onset.
Flange rotation (deflection) — caused by thermal and mechanical loads — causes the flange ring to rotate about its hub, reducing compression at the gasket seating face in a non-uniform manner. The 2018 Wuhan Engineering University patent identifies maximum deformation loci at the cone-neck to cylinder junction and the cone-neck to flange disc junction, computing three partial deflection angles incorporating creep effects. For further context on pressure vessel integrity standards, see guidance from NIST and the UK Health and Safety Executive.
- Petrochemical and process industry pipelines
- Power generation and steam systems
- Gas turbine and aerospace exhaust joints
- Nuclear pressure vessel closures
- Sealing material test methodology
Four Engineering Approaches to Managing Stress Relaxation
Patent and literature evidence organises into four distinct clusters, each addressing a different aspect of the coupled thermal-mechanical failure mode.
Creep-Relaxation Modelling and Time-Dependent Leakage Prediction
Standard room-temperature design codes such as ASME PVRC methods do not capture time-dependent behaviour. Researchers have developed coupled thermal-structural finite element models incorporating creep constitutive laws for bolts, gaskets, and flanges. The 2023 Hefei General Machinery Research Institute patent uses ABAQUS sequential coupled thermo-structural analysis to extend the ASME PVRC ROTT room-temperature leakage method to long-period high-temperature service. The 2025 ECUST patent focuses specifically on the gasket as the primary failure-initiating element. A 2015 literature study establishes a method to determine stress relaxation function parameters for viscoelastic gaskets and links those parameters directly to vessel leakage probability.
Gasket creep-relaxation parameters poorly characterised above creep onsetDifferential Thermal Expansion Compensation — Sleeve and Material Methods
Two competing design strategies address the CTE mismatch root cause. The 2021 steam generator study proposes sleeve inserts of higher CTE material placed between flange-nut and bolt-head interfaces to nullify load loss as temperature rises. The 1957 British Thomson-Houston patent — the earliest in the dataset — established design principles for high-temperature fasteners addressing creep-induced load loss. Siemens Energy’s 2021 WO patent documents that during gas turbine transient operation, flanges heat faster than bolts, causing cyclic preload variation; plastic deformation and creep of the flange at steady state further reduce clamp load.
Sleeve inserts reverse differential expansion effectMechanical Compensation Devices — Disc Springs and Compliant Elements
Rather than designing around CTE mismatch, this cluster introduces elastic compensation elements into the bolt stack. Disc springs (Belleville washers) exploit their high spring rate at small deflection to absorb creep-induced deformation while sustaining bolt load. Jiangxi Mingyuan Electric Co., Ltd. filed patents in 2015 and 2018 deriving analytical expressions for creep displacement of bolt, gasket, and flange ring and incorporating disc-spring stiffness coefficient (Kw) into the compatibility equation. ITT Engineered Valves’ 2014 US patent demonstrates the elastomeric member principle across non-metallic diaphragm valve applications to provide substantially constant sealing force regardless of dimensional changes caused by temperature fluctuations.
Disc springs — most proven mechanical mitigation in datasetHigh-Temperature Tightness Evaluation Methods and Design Codes
This cluster covers systematic engineering methods for evaluating whether a flange joint will remain leak-tight over its intended service life under combined creep, thermal, and pressure loading. The 2018 Wuhan Engineering University patent presents a full workflow: compute three partial deflection angles incorporating creep effects, solve the deformation compatibility equation for time-dependent gasket stress, and compare against ASME rotation limits and minimum seating stress to determine safe operating life. The 2020 critical energy method paper critiques standard methods for omitting bending moment effects on bolt strength, residual stresses, and gasket relaxation over time. Learn more about PatSnap solutions for regulated-industry IP analysis.
ASME codes do not capture time-dependent gasket relaxationFiling Activity and Technology Cluster Distribution
Patent filing cadence and cluster weighting derived from the retrieved dataset of 18 directly relevant records.
Filing Activity by Period
Chinese institutions dominate filings from 2010 onwards; European and US activity concentrated in structural/geometric design adaptations.
Technology Cluster Share
Creep-relaxation modelling is the most active cluster; mechanical compensation devices represent the most mature mitigation approach.
High-Temperature Flange Tightness Evaluation: Step-by-Step
Based on the Wuhan Engineering University 2018 patent, the systematic evaluation workflow for determining safe operating life of a high-temperature bolted flange joint.
What the Patent Landscape Signals for R&D and IP Teams
Four strategic observations derived from the 1957–2025 dataset for organisations active in pressure vessel design, sealing technology, or digital inspection tooling.
Creep Modelling Must Be Multi-Component
No single component — bolt, gasket, or flange — alone determines stress relaxation. Deformation compatibility of all three simultaneously governs gasket residual stress evolution. R&D teams should ensure computational models incorporate all three creep terms or risk systematically overestimating joint service life.
Chinese Institutions Hold the Densest Recent IP Position
With at least 7 directly relevant patents filed by Chinese universities and research institutes between 2010 and 2025, organisations entering this space should conduct freedom-to-operate analysis against Chinese patents, particularly for analytical and computational methods and disc-spring compensation designs.
Three Forward Directions Signalled by 2021–2025 Filings
| Direction | Key Patent / Source | Assignee | Year | Core Innovation |
|---|---|---|---|---|
| Long-Period Service Life Prediction with Integrated Creep Models | Time-Dependent Leakage Rate Prediction Method | Hefei General Machinery Research Institute | 2023 CN | ABAQUS sequential coupled thermo-structural analysis extending ASME PVRC ROTT method to long-period high-temperature service |
| Gasket Creep-Relaxation Predictive Modelling | Gasket Creep-Relaxation Performance Prediction Method | East China University of Science and Technology | 2025 CN | Focuses on gasket as primary failure-initiating element; high temperature accelerates gasket creep-relaxation and aging, reducing elasticity and sealing capacity |
| Thermal Stress Decoupling in Flange Geometry | Long-Arm Flange Design for Thin-Walled Parts | Solar Turbines Incorporated | 2023 US | Decouples thermal stress from mechanical bending stress via extended arm geometry; structural design approach rather than material or compensating-element approach |
Siemens Energy Global GmbH & Co. KG’s 2021 WO filing addresses the specific challenge of transient thermal gradients in gas turbine flange joints — where plastic deformation during startup and creep during steady state combine. This signals increasing attention to joint management under cyclic rather than purely static thermal loading. Explore PatSnap analytics for gas turbine IP landscape analysis.
Stress Relaxation in Bolted Flange Joints — key questions answered
Stress relaxation in bolted flange joints is a time-dependent mechanical failure mode driven by creep in bolts, gaskets, and flange bodies at elevated temperature, causing progressive loss of clamping force and ultimately leakage.
The four interacting phenomena are: differential thermal expansion between bolts, flanges, and gaskets; creep of bolts, gaskets, and flange body; stress relaxation of the gasket (particularly viscoelastic types such as spiral wound, flexible graphite, and elastomeric); and flange rotation (deflection) caused by thermal and mechanical loads.
Disc springs (Belleville washers) are introduced into the bolt stack to maintain approximately constant gasket contact stress as creep and thermal relaxation consume the initial preload. Their high spring rate at small deflection absorbs creep-induced deformation while sustaining bolt load. The analytical model treats disc-spring stiffness coefficient (Kw) as an additional term in the joint stiffness balance.
The problem is of critical importance across petrochemical, power generation, and steam engineering industries, where joint integrity directly determines process safety and environmental compliance. Gas turbine and aerospace applications are also affected, with gas turbines imposing the most severe transient thermal gradients.
Standard room-temperature design codes such as ASME PVRC methods do not capture time-dependent behavior. The 2020 critical energy method paper explicitly identifies that current acknowledged calculation methods do not account for gasket relaxation over time, bending moment effects on bolt strength, or residual stresses.
China is the dominant jurisdiction with at least 7 directly relevant patents from Nanjing Institute of Technology (2010), Wuhan Engineering University (2 filings, 2015 and 2018), Jiangxi Mingyuan Electric Co., Ltd. (2 filings, 2015 and 2018), Hefei General Machinery Research Institute (2023), and East China University of Science and Technology (2025). The United Kingdom holds the earliest filings from 1957 and 1958.
PatSnap Eureka searches patents and research literature to answer instantly.